Cellulose acetate yarn and process



Oct. 30, 1945. R. M. HOFFMAN V 2,337,791

GELLULOSE ACETATE YARN AND PROCESS Original Filed June 11. 1941 4 q 6 ,l 1 7 v 3 b J W21 H Cell heah'zgg 170% 1 14 b I c s INVENTOR. Robert M. Hoffman ATT may Patented ct. 35%, 1945 2,387,791 7 v CELLULDSE hearers YARN sun rnocnss Robert M. Hofiman, Waynesboro, Va, assignor to E. I. du Pont de Nemours & Company, Wilmington, Del, a corporation of Delaware Original application June H, 1941, Serial No,

Divided and this application October 30, 1943, Serial No. 508,433

I 1 Claim. ($1. 18-54) This invention relates to the manufacture of organic acid ester cellulose filaments, and more particularly to new and improved cellulose ace tate filaments especially suited for use in rug pile fabric, and to the process by which the filaments are formed.

This application is a division of my copending application Serial No. 397,629 filed June 11, 1941, now U. S. Patent 2,341,615.

Processes and apparatus have heretofore been developed and successfully used for the spinnin of cellulose acetate filaments of large denier, i. e. denier of 15 and upwards to 40 denier or more.

There has also been described inthe prior art, filaments of cellulose acetate which are substantially round and smooth. (By substantially round and smooth is meant that the maximum and minimum. cross-sectional dimensions at a given point are not greatly difierent and that the contour of the filament cross-section is relatively free of sharp indentations or crenulations.) aments having this substantially round and smooth cross-section do not have the capacity to hold dirt and do not become more or less perina- -nently soiled as do filaments having highly crenulated cross-section. Furthermore, when the filaments or fibers are more substantially round, they have improved stiffness and resilience as com-= pared with filaments and fibers wherein the maxiinum cross-sectionaldimension is several times, for example, or even 20 times, the minimum cross-sectional dimension.

Cellulose acetate filaments of a high degree of toughness are likewise known. In this connection it should be observed that toughness is not synonymous with tenacity. Yarn which has a high degree of toughness is not necessarily a yam properties must be present together.

a soft, warm, and at the same time a crisp,

spriney, resilient feel, have also been described.

However, while cellulose acetate filaments of An obj ect of this invention, therefore, is to furnish filaments of cellulose acetate which are of large denier, which have a substantially round and smooth cross-section, which have ahigh clegree of toughness, and which can be made into yarns which have the soft, lively feel requisite in rug pile.

A further object resides in a process for forming filaments of cellulose acetate which will have the desirable combination of properties. enumerated above.

These and other objects will more clearly appear hereinafter.

I have found that a filament fulfilling the requirements hereinabove stated can be produced by spinning cellulose acetate from a solution inc suitable volatile solvent by the dry or evaporative method while correlating and mainta'hiins, in a 1312113115? to be fully explained'the following factors:

1. The concentration of the cellulose acetate in the spinr'iing solution. 2. The temperature of the just prior to extrusion.

3. The temperature of the cell. 4. The concentration of the solvent vapor within the cell.

spinning solution 5. The size'and spacing of the orifices in the spinneret.

6. The drawoff speed.

It is not necessary that any-one of these factors be maintained at any specific value, but a reasonable range of values will be found satisfactory providing the other factors are suitably adjusted although there are certain limits of conditions within which the spinning operation must be carried out to obtain satisfactory results. For

instance, the concentration of solvent vapor Within the cell must be kept very high if satisfactory cross-sections are to be obtained. For instance, when using acetone as the solvent the concentration of solvent vapor within the cell must be maintained above 1500 gramsof acetone per cubic meter of atmosphere or above about 78% solvent vapor by volume. This is probably the most important of all the factors, but even so, unless the otheriactors are maintained within the limitsjgiven' below, continuity of spinning cannot be maintained and/oaths physical char- 1 acteristics of the product produced will not be floor covering materials.

taining not more than 5% of water should be maintained within the limits 01-25% to'32%. The solution temperature just prior to extrusion should be maintained within the limits of 50 C 'tained within the limits of from 85 C. to 115 CI The hole diameter or the orifices of the spinning I Jet should be maintained within the limits of 0.10 to 0.30 millimeter. The stretch ratio, computed as the ratio of draw-oifor wind-up speed oi the yarn to the jet velocity of the spinning solution as it issue from the orifices in the-spinneret, may be varied quite widely, for instance from 0.8

'to 6 or ,7. Best results are obtained when the With an increased spinning speed, it is necessary to raise the cell temperature to increase the amount of solventremoved from the yarn in'a given time. To compensate for these two factors (higher concentration of cellulose acetate in the spinning solution and higher spinning speed) which tend to increase the filament tension, the aspiration should preferably be kept low and the spinning solution temperature reduced. The best results at higher spinning speeds are generally obtained with higher concentration of cellulose acetate in the spinning solution.

Proper correlation of the determining factors are further illustrated by the following: In spinning a solution comprised of 28% cellulose acetate (about 54% combined acetic acid), 2% water, and 7.0% acetone, it is preferred that the concentration of acetone vapor within the cell be maintained between 90% and 95% by volume, that the orifices within the spinneret be from 0.10 to 0.20 millimeter in diameter, that the temperature of the spinning solution just prior to extrusion be maintained at about 60 C. and the cell temperature at 89. C. (or, with a solution temperaturr at 55 C., the cell temperature should. F

' temperature of about 57 C., the cell temperature should be maintained at about 90 C. (If thesolution temperature is'less, say 52 C., the cell temp rature should-be maintainedat about 115 C.) To prevent filaments from sticking together in such as is described "herein, it is necessary to' have the orifices in the spinneret spaced at somewhat greater distance than is used for the normal methpclof evaporative spinning (the minimum hole spacing in a spinneret for .producing a -fllament product is about 7.5 millimeshould be at least 8.0 millimeters and preferably more) In order to, regulate and maintain the various spinning conditions within the desired narrow to- 70 C. The cell temperature should be main- "5 aspiration rate are-desirable to compensate for the reduced amount of solvent tobe evaporated.

limits, I have found it necessary to devise a radically new type of spinning cell in which to carry out the process. The structure of the spinning cell and the advantages thereof with respect to the practice of my process is best understood by reference to the accompanying drawing wherein: Fig. 1 is a diagrammatic representation or the spinning cell in vertical cross-section together ,with the associated filament and solvent draw-on elements, and I Fig. 2 is'a typical cross-section of the filament produced by my process.

Referring to Fig. 1 of the drawing; l designates a metering pump which delivers the spinning olution at a constant rate to a water jacketed spinning head 2, wherein the solution is heated i to the desired spinning temperature before extrusion through spinneret 3. In the spinneretv assembly, a filter pack 3A of conventional design is used to develop back pressures of from 300 to the influx of anyair. Inthe upper part 01' the Joell also in the vicinity ofthe spinneret, a short pipe 5' is provided as shown to serve as a holder for an orifice i of from 0.00023to 0.0012 square inch in areaor, if circular, or 0.015 to 0.040 inch diameter which'is used to limit the amount of air entering the cell; and thus maintain a high concentration of solvent vapor in the evaporative medium in the majorportion o! the cell. The enspinning in a high concentration of solvent vapor ters. In spinning a larger number of filaments tire cell 0 and especially the upper portion thereof should be well sealed to prevent influx of air other than through orifice I in order that the 'solvent vapor concentration will be precisely consteam or any other suitable heating medium.-

At the bottom of the cell is a tube opening I to allow the filaments to be withdrawn. This is sufllciently small in diameter (preferably about inch) and sufficiently long (preferably about 3 to 4 inches) to permit the development of a par- ,tial vacuum of from V; to 6 inches of water within the. cell for the'purpose of controlling the amount of air entering through orifice 5 without necessitatingexcessive aspiration that would cause an undesirably ,high gradation of acetone vapor concentration from the top to the bottom of the cell. The amount of air drawn in through opening 8 is approximately times the amount drawn through orifice 5, but since this is immediately removed and mixes with the solvent vapor only in the lower-most portion of the cell, it has no undesirable eiIect on the filaments being spun. vThe partial vacuum within thecell may be conveniently developed by means of a blower I! which develops a partial vacuum in mixing chamber ll isolated from the outside and the rest of the system .by flame arresters 8 and II; By means of this partial vacuum in mixing chamber ii, anis drawn from the room through orifice II andthe vapor-air mixture from the cell through 45 can best be determined experimentally for their size will depend on the design of the aspiration system and the capacity of, blower I3. By this sort of aspiration arrangement, enough air is admixed with the exit gases and vapor from the cell to dilute the acetone vapor to a point below its lower .explosive limit before collecting it in the.main header pipe to acetone recovery.

(The

acetone-air mixture in the main body of the cell is in the upper non-explosive range.) The yarn after leaving the cell through opening 8 may be conveniently taken up by mechanism i4 consisting of a yarn guide e, a roll for finish application a, feed ,roll b, take-up bobbin 0, and a driving roll for the take-up bobbin :2.

By means of the simple arrangement for regulating the influx or air into the upper part of the spinning cell, the concentration of solvent vapor in air which comprises the evaporative medium inside the cell may be easily but precisely controlled. For instance, by using a small size orifice 5, say 0.015 inch in diameter, and a slightly reduced pressure inside the cell amounting to $4; inch of water column, the flow of air into the upper part oflthe cell will be found to be uni-.

form and constant at about three liters per hour. By increasing the pressure differential between the inside and the outside of thecell and the size of orifice 5, the flow of air into the upper part of the cell may be increased up to 100 liters per hour or more. The amount of air to be admitted into the upper part of the cell will, of course, depend upon the concentration of acetone vapor desired within the cell, the rate of spinning, the concentration of the spinning solution, the temperature of the cell, etc. If desired, instead of having orifice 5 communicating with the outside atmosphere, it may be directly connected 7 to a source of gas other than air, for instance, an

inert gas comprised ofe mixture of nitrogen and carbon dioxide which may be produced by any of the well known inert gas machines now on the market.

Although the means the air intake of 0.025 inch and maintaining a slight partial vacuum inside of the cell amounting to 1% inches of water column, suificient air I was drawn in at 37 C. to maintain an acetone concentration of 1790 grams per cubic meter (when measured at 70 C., and 760 millimeters) in the evaporative medium in the cell or 93.4%

of acetone by volume. The extrusion rate of the spinning solution was such that with a wind-up speed of 125 yards per minute, a 100-denier, 2T0- filament yarn was produced.

The yarn so produced, after conditioning at a constant humidity of 65% R. H. and a temperature of 75 F., had a dry strength of 1.00 gram per denier and a dry elongation at the breaking point of 47% as measured on a Scott inclined tester. The cross-sectional shape of the filaments was peanut-shaped (see Fig. 2) with the minimum diameter of an average cross-section about 30% of the maximum diameter of the average cross-section. The contour of the crosssection was generally smooth. The yarn had a pleasing .handle, good uniformity, and could be satisfactorily handled on textilemachinery. When woven as the pile incarpet, it was found to have the desired resilience and other desirable characteristics needed in this type fabric.

A-s'imple test which distinguishes my yarn from large denier yarns spunv according to the usual procedures is carried out as follows: A

, sample of the yarn of this example is soaked for two minutes in 70% denatured alcohol at 15 C. and stretched 25%, washed in water, dried, and is then immersed in a boiling solution of 10% denatured alcohol inwater. As a result of this treatment, the yarn spontaneously elongates at least 25%; Known large denier yarns do not respond in this'fashion.

hereinbefore described for controlling the concentration of solvent vapor in the evaporativemedium inside 01' the cell may be used very advantageously, other means as will be readily apparent to one skilled in the art can, of course, be substituted. The only requirement is to precisely control-the concentration of solvent vapor aroundthe filaments through their major portion of their travel through the spinpreviously described. The spinning solution Example 11 A cellulose acetate spinning solution having a viscosity of 400' poises when measured at 40 C. and'comprised of 25% celluloseacetate (havin an acetic acid content of about 54%) and 75% acetone was spun into 200-denier, 10-filament yarn using this same type spinning cell. In this case the spinning solution temperature was 70 C., the cell temperature 88 C., and suflicient air was drawn into the upper part of the cell through orifice 5 to maintain an average acetone concentration of 1850 grams per cubic meter or about 96.3% of acetone by volume (measured at70 C.

" The, yarn-so produced had a dry strength of 1.26

heated at C. was extruded through a 20-hole spinneret, each hole being 0.20 millimeter diameter andv the holes space 8.0 millimeters apart. The inner wall of the jacketed portion of the cell was heatedlto 88 C. and using an orifice (5) at grams per denier and a dry elongation of 56%- when conditioned and measured at R. H.

' and at F. The cross-section was substantially the same as shown in Fig. 2 and the yarn responded to the spontaneous elongation test of Example I. Example III The spinning solution described in Example II was extruded at a solution temperature of 50? 0. through a 20-ho1e 'spinneret, the holes being 0.3 millimeter diameter, into the cell previously described which cell body was heated to a tern perature of 115 C. The evaporative atmosphere within the cell contained an average acetone concentration of 1820 grams per cubic meter or about of acetone by volume (measured at 70 C.

. The solution (after filtration, resting, etc.) was heated to 60 C. and was extruded through-a spinminute, the production of a 400+denier, zo-filament yarn necessitated the same rate of solution v delivery through each orifice, but in view or the much larger size openings in the spinneret (the area being more than three times that given un- 5 der Example II). the jet velocity was less than Va or the stretch ratio was about 7.3. The characteristics of the yarn so'produced'was generally the same as in Example I, the dry'tenacity of the yarn being 0.98 gram .per denier, the dry elongation 51% and the filament cross-sections similar tothat shown in Fig. 2.

Example IV T The spinning solution described under Example II heated to 60 C. was extruded through a -hole spinneret, the diameters ofthe holes being 0.20 millimeter, in the spinning cell previously described whichwas heated to a tempera ture of 88 C.- Air containing 1600 grams of ace- 20 tone per cubic meter or about 83.3% of acetone by volume (measured at 70 C. and 760 millimeters) constituted the evaporative medium. In this case where the yarn draw-oil. speed was 100 yards per minute to produce a 400-denier, 20-filament yarn, there was a'stretch ratio of 3.2. The

y'arn so produced had a dry tenacity of 0.97 gram parts of acetone and the viscosity of the solution 5 as measured at 40 C.'was found to be 1500 poises.

neret'having 20 holes, each hole being 0.12 millimeter diameter, into the spinning cell previously 40 described and heated to 88 C. while maintaining 'an average concentration 01 1810 grams of acetone per cubic meter or about 94.3% of acetone by'volume (measured at 70' C. and 760 millimeters) as the evaporative medium inside the 5 cell. The rate of extrusion was so adjusted that at a wind-up of 125 yards per minute. the yarn had a final denier of 400. In this case,'the stretch ratio was 1.4.

The yarn so produced had a dry tenacityof 5 1.20 grams perdenier, a dry elongation of 51% and a cross-section very tothat or 1 1g. 2.

. Example VI v The spinning solution of Example V heated to 55 55 C. was extruded through a spinneret with twenty 0.20 millimeter holes in the-spinning cell of this invention heated to 115' O. and contain- 'ing sufiicient .air so that a concentration of 1870 grams of acetone per cubic meter or 97.4% of acetone by volume was maintained as the. evaporative medium. The solution delivery rate was adlusted toyield a 400-den1eryarnat a draw-oft speed at 150 yards per minute which resulted in a stretch ratio of 8.9. The yarn so produced had a dry tenacity of 0.95. grainv per denier. a dryspinneret, each hole being 0.14 millimeter di- .7

' isfactory "handle."

assmor meter and spaced 10 millimeters apart, into the I spinning cell of this invention which was heated to 88 C. while the evaporative medium therein was maintained ata concentration of 1710 grams millimeters). The solution delivery rate was ad- Justed'to yield 'a ZOO-denier, lo-filament yarn at a wind-up speed of 114 yards per minute. The stretch ratio was 1.6. The yarn so produced by this example had a dry tenacity .of 1.26 grams per denier, a dry elongation of 44% and filament cross-section very similar to Fi 2.

While my invention is described primarily from the standpoint of spinning acetone-soluble cellulose acetate from an acetone solution or anpile in carpet or like materials'such as set forth earlier in this description can be readily produced. The spinning cell of this invention en- 'ables uniform spinning conditions to be maintained over long periods of time, and whenever a difierent yarn (filament size or count, for example) is desired a change in spinning conditions can be efiected easily. Even though a number of important factors are involved and maintaining these factors within exceedingly narrow limits for any given production is' essential, filaments having the desired uniiormeharacteristics are readily produced.

Not only does my invention satisfy all the essential requirements for a good carpet pile filament or fiber, but under these preferred conditions, a yarn having large denier filaments shaped in cross-section like a peanut, a pinched-in ellipse, or even at times bean-shaped or elliptical and with a relatively smooth contour can be produced which has a characteristic sparkle, a high degree of toughness, and an altogether sat- When .these filaments or fibers are incorporated as the pile in rugs or carpets, they very materially enhance the appearance of the rug or carpet.

, It is to be understood, of course, that the above" description is for purposes of illustration only,

and that my invention is not limited to the exact conditions and structure herein set out but is subject rather to all variations and modifications falling'within the terms and spirit thereof as defined in the following claim. 4

. Iclaim: I

A process for dry-emailing filaments of cellulose acetate which comprises heating an acetone solution containing mm about 25% to about 33% by weight of cellulose acetate to a temperature or from about 50 to about C., and extruding said heated solution through circular orifices of from about 0.10 to about 0.30 mm. in diameter into anatmosphere maintained throughout ate temperature or from about to about 115 C. and comprising throughout at least 1500 grams of acetone vapor per cubic meter of atmosphere.

ROBERT M. HOFFMAN. 

